Multi-colored silk screen printing presses are used to print multi-colored images on substrate materials such as a T-shirts, sweatshirts, posters, etc. The substrate material is mounted on one of several pallets which typically extend radially from an indexed turret. The turret is rotated to move the pallets among a plurality of print units located peripherally around the turret. Each of the print units prints a different color, to produce a multicolored image on the substrate material.
Silk screen printing machines have one or more heat curing stations intermingled among the several print stations. The heat curing stations use electric resistance heating elements, such as a bank of quartz flash lamps, to quickly heat previously printed ink and sufficiently cure the ink before printing another color at a subsequent print station. It is not always necessary to cure a previous layer of ink before printing a subsequent layer. This is true when the previous layer is a thin layer of ink. On the other hand, it is almost always necessary to cure a first base layer of ink printed on the substrate material (e.g. a base layer printed on a T-shirt). Also, it may be desirable to cure after applying a subsequent heavy layer of ink, or even after applying two or more thin layers of ink consecutively.
A bank of quartz flash heater bulbs in a cure unit is capable of producing temperatures up to about 1200.degree. F. To cure the ink, the bank of flash lamps is placed in close proximity (e.g. 2-3 inches) above the image on the printed material, and the bank of quartz flash lamps is powered to supply extreme heat and raise the temperature of the ink to a curing temperature, or slightly above. The curing temperatures for different types of inks can vary, but generally range from 200.degree. F.-350.degree. F. Controls for prior quartz flash cure units typically turn the bank of flash lamps off after a preselected time period that is set by an operator of the press by adjusting a potentiometer.
If the quartz flash lamps are on too long, the lamps can scorch the ink or the underlying substrate material, or can otherwise damage the final product. Press operators often adjust the potentiometer that controls the activation time for the quartz flash lamps on the basis of trial and error. This can present a problem because heat transfer characteristics on the system vary with respect to many factors, including the characteristics of the underlying substrate material, the type of ink, as well as the operating conditions surrounding the curing unit. For instance, it may take the curing unit 5-7 seconds to raise the ink temperature from room temperature to a cure temperature at a first curing station, but only 2-3 seconds at a subsequent curing station after the item has been heated. In addition, each particular curing station typically heats faster as the machine continues in operation because residual heat does not dissipate completely. Since the press operators do not know the actual temperature of the ink, it is difficult for the operators to accurately regulate the activation time for the quartz flash units.
There have been some efforts in the industry to promote dissipation of the residual heat by the use of fans and the like. However, these methods tend to increase the required curing time and can even slow production of the overall printing process.